Apparatus for forming a tubular frame member

ABSTRACT

An apparatus for bending a tube blank having an outer diameter, comprising: an inner bending die having an arcuate outer surface which has a first radius from an axis; a wiper shoe having an inner surface, said shoe disposed and adapted to trap a tube blank between said inner surface and said outer surface; holding means for holding a first portion of the blank against said inner die; limiting means for limiting movement of said shoe to rolling about an arc around said axis, said arc having a second radius from said axis which is approximately between said first radius and said first radius plus said diameter; and, moving means for moving said shoe around said axis, and around the blank thereby bending a second portion of the blank around said outer surface; and sealing and pressurizing means for sealing the blank and for hydraulically pressurizing the interior of the blank to a sufficient pressure to allow moving means to bend a second portion of the blank around said outer surface, said pressurized liquid acting like a flexible mandrel to ensure uniform, non-buckling deformation of the tube, substantially without distorting the cross section of the second portion.

REFERENCE TO RELATED APPLICATIONS

This application is a division of patent application Ser. No. 08/263,325filed Jun. 21, 1994, now U.S. Pat. No. 5,499,392 which is a division ofpatent application Ser. No. 08/077,616 filed Aug. 23, 1993 and issued asU.S. Pat. No. 5,353,618, which is a division of patent application Ser.No. 07/837,081 filed Feb. 12, 1992 and issued as U.S. Pat. No.5,239,852, which is a continuation of patent application Ser. No.07/482,782 filed Feb. 21, 1990, now abandoned, which is acontinuation-in-part of patent application Ser. No. 07/398,272 filedAug. 24, 1989, now abandoned, all of which are hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to the field of cold forming tubularmaterials and in particular to an apparatus and method for forming acomplex-shaped tubular frame member from a tubular blank.

BACKGROUND OF THE INVENTION

The principal frame design for automobile frame members is of the "box"type construction for strength and load bearing purposes. These framemembers often have great variation in both the horizontal and thevertical profile. The cross-section of such tube members also oftenvaries rather extremely from approximately a square cross-section, to arectangular cross-section to a round cross-section to a severelyflattened cross-section, and to any irregularly shaped combination ofthe above. While some simple, large radiused profiles with varyingcross-sections have been obtained by cold or heat forming a generallycylindrical tube blank, most current manufacturing methods produce thecomplex-shaped box section tube member by fabricating two "U" sectionstampings which are then welded together to form the finished part.Unfortunately, material and labor consumption in these processes isenormously inefficient. Also, evidence appears to show a significantnoise level reduction where the box section frame member is formed froma tubular blank rather than the welded, double "U" section stampings.

The general operations of bending, stretching, depressing and radiallyexpanding a tube blank, with or without a mandrel, are known. For themajority of metals, it is fairly easy to bend small diameter tubing intoan arc having a large radius. But as the diameter of the tubingincreases and the radius about which it is to be bent decreases, thetube bending process requires some combination of compression at theinner bending radius of the tube and stretching at the outer radius.Although the outer bending surface of the tube may be stretched to thefull extent of the materials rated elongation characteristics, cannotsatisfactorily bend a tube with a given diameter about a relativelysmall bending radius without encountering severe buckling at the innerbending surface or undesirable deformation at the outer bending radius.Some have achieved bending tubes with a certain diameter aboutrelatively small bending radii by controllably dimpling or allowingcontrolled rippling of the inner tube surface thereby creating lessstretching of the outer tube surface.

Other examples of methods for bending a tube are shown in U.S. Pat. No.4,704,886 shows internally pressurizing a tube blank, gripping theopposite ends of the blank and applying longitudinal tension at the endswhile applying a lateral force against the blank to bend the blank. U.S.Pat. No. 4,567,743 shows depressing regions of the tube blank and thenexpanding the blank within a complementary shaped cavity formed by apair of dies. U.S. Pat. No. 4,829,803 discloses forming a box-like framemember by internally-pressurizing a preformed tubular blank, closing apair of die halves around the blank to partially deform the blank withinmating die cavities, and then increasing the internal pressure to exceedthe yield limit of the wall of the blank to expand the blank intoconformity within the mating die cavities. In the '803 patent, theplanar mating surfaces of the die halves are perpendicular to the sidewalls of the cavities, and the patent teaches that by providing acertain internal pressure to the tubular blank, upon closing the diesections, the blank will spread evenly throughout the cavity and willnot be pinched between the closing, mating surface portions of the dies.This procedure may prove satisfactory where the width of the diecavities is much greater than the height. However, where the height ofthe die cavities is much greater than the width, as is often the casewith complex-shaped, box section frame members, the tubular blank willsimply not be pushed into the deep recesses of the cavity withoutpinching between the mating die halves.

What is needed is an apparatus which will form a tubular blank into abox section frame member having variations in the vertical andhorizontal profile and in the cross-sectional configuration.

SUMMARY OF THE INVENTION

Generally speaking, the present invention provides an apparatus andmethod for forming a tubular blank into a box section frame memberhaving variations in both the horizontal and vertical profile and in thecross-sectional configuration.

The process basically consists of two steps. First, a straight roundtube of a pre-cut length is internally pressurized and bent in one ormore locations along its length. This preformed tube is then located onthe lower half (the die) of a punch and die and pressurized again. Theupper half (the punch) then closes completely, producing the finallyformed frame member. Before the tube is preformed, its ends areburnished to remove the cutting burr and to radius the outside, leadingedge of the blank.

In the preforming stage, sealing units and the forming tools arecompletely submerged in an aqueous bath, allowing the tube to "fillitself" when placed therein. The sealing units then simultaneously sealand pressurize the blank and the blank is tangent bent, forming a pairof legs in horizontal profile. Inner and outer dies then close upon thelegs, forming additional multiple bends in the horizontal plane. Thispreformed tube is then placed upon a lower, upwardly facing stuffingledge of the die, the die defining a vertical, punch engaging wall whichsmoothly transitions at its bottom into the ledge, the ledgetransitioning at an acute angle into a first vertical heel. A punchdefines a vertical, die engaging wall which smoothly transitions at itstop into an upper, downwardly facing stuffing ledge, the upper ledgetransitioning at an acute angle into a second vertical heel, and theupper and lower ledges being in constant vertical alignment. The punchis adapted to ram down to a tube trapping position wherein the blank isdisposed upon the lower ledge and the upper and lower ledges and the dieengaging and punch engaging walls together define an enclosed cavitywhich traps the blank therein. The blank is then simultaneously sealedand pressurized to a less-than-burst pressure. The punch is then moveddownward, bringing the upper and lower stuffing ledges to a final dieposition, thereby forming the finally formed frame member. To the extentthe cross-sectional perimeter of the blank is less than thecorresponding cross-sectional perimeter of the cavity formed by themutually cooperating ledges, the internal pressure of the tube isincreased to a pressure sufficient to cause outward deformation of thetube wall into the remaining recesses of the ledges. Like the preformingstage, the die components are sufficiently submerged in an aqueous bathso that upon placement of the preformed tube upon the lower ledge, thetube will "fill itself", facilitating the sealing and pressurization ofthe tube.

It is an object of the present invention to provide an improved tubeforming apparatus.

It is another object of the present invention to provide an apparatuswhich will form complex-shaped frame members from tubular blanks.

It is another object of the present invention to quickly andeconomically produce shaped frame members from tubular blanks.

Further objects and advantages of the present invention will becomeapparent from the following description of the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side, elevational view of the apparatus for forming atubular frame member in accordance with the preferred embodiment of thepresent invention.

FIG. 2 is a one-half plan view about centerline of symmetry 18 of theapparatus of FIG. 1.

FIG. 3 is a side, elevational view of the blank feeder and burnishingstation I of the apparatus of FIG. 1.

FIG. 4 is a plan view of the blank feeder and burnishing station I ofFIG. 3 with push down cylinders 58 omitted for clarity.

FIG. 5 is a side view, partly broken away, showing the operation of thepush-up cylinder of blank feeder and burnishing station I of FIG. 3.

FIG. 6 is a side, cross-sectional view of the burnishing tool of theblank feeder and burnishing station I of FIG. 4.

FIG. 7 is a plan view of one-half of the tangent bend andprehydroforming station II of the apparatus for forming a tubular framemember of FIG. 1, with the wing and dies shown in the open and retractedpositions.

FIG. 8 is a cross-sectional view of one side of the outer die 96 of FIG.7 taken along the line 8--8 and viewed in the direction of the arrows.

FIG. 9 is an enlarged view of the tangent bend and prehydroformingstation II of FIG. 7, and shown with the wing and dies in the closed andextended positions.

FIG. 10 is a side, cross-sectional view of the tangent bend andprehydroforming station II taken along the line 10--10 of FIG. 9 andviewed in the direction of the arrows.

FIG. 11 is a side, cross-sectional view of the tangent bend andprehydroforming station II taken along the line 11--11 of FIG. 9 andviewed in the direction of the arrows.

FIG. 12 is an enlarged, partly cross-sectional view of the sealing toolof FIG. 9.

FIG. 13 is an end, elevational view of the final hydroforming stationIII of the apparatus for forming a tubular frame member of FIG. 1.

FIG. 14 is a plan, partly cross-sectional view of the tub, die, andsealing units of the final hydroforming station III of FIG. 13.

FIG. 15 is an end, cross-sectional view of the punch and die of thefinal hydroforming station III of FIG. 14, shown in the tube trappingposition, taken along the line 15--15 of FIG. 14 and viewed in thedirection of the arrows.

FIG. 16 is a side, cross-sectional view of the punch and die of FIG. 15,in the tube trapping position, and taken along the lines 16--16 of FIG.14 and viewed in the direction of the arrows.

FIG. 17 is an enlarged, end view of the final hydroforming station IIIof FIG. 13 and showing the transfer system.

FIG. 18 is an enlarged, cross-sectional view of a portion of the punchand die of the final hydroforming station III of FIG. 15.

FIG. 19 is an enlarged, partly cross-sectional view of a combinationburnishing and sealing unit in accordance with another embodiment of thepresent invention.

FIG. 20 is an enlarged, cross-sectional view of the combinationburnishing and sealing tool of the combination burnishing and sealingunit of FIG. 19.

FIG. 21 is an enlarged, cross-sectional view of a portion of thecombination burnishing and sealing tool of FIG. 20, showing theconverging end 309 of gland 308.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiment illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

Referring now to FIGS. 1 and 2, there is shown an apparatus 10 forforming a complex shaped frame member (that is, one having a varyingvertical, horizontal and/or cross-sectional profile) for an automobilein accordance with the preferred embodiment of the present invention.The invention described herein, however, may be adapted to form tubularframe members for a variety of structures. Apparatus 10 comprises aseries of stations, namely a blank feeder and burnishing station I, atangent bend and prehydroforming station II, a final hydroformingstation III, and an end cropping and ejection station IV. Except whereindicated, apparatus 10 and blank 11 are horizontally symmetrical aboutcenterline 18.

Generally, apparatus 10 delivers a tube blank 11 from hopper 12, downramp 13 and into liquid-filled tub 15 of station II. In tub 15, blank 11is tangent bent and prehydroformed into preformed tube 16. A first liftmechanism 17 mounted on shuttle 14 of transfer system 19 lifts tube 16from tub 15, transfers it laterally to an idle station 20, and places itupon idle station table 21. Shuttle 14 then translates back to its idleposition (whereby mechanism 17 is midway between station II and idlestation 20, second lift mechanism 22 is midway between idle station 20and station III, and third lift mechanism 23 is midway between stationIII and station IV). While no machining occurs upon the tube 16 atstation 20, each of stations I-IV then performs its respective operationupon the blank 11, tube 16 or finally formed frame member 25 located atthat station. Shuttle 14 then translates to its rearward position (tothe left as shown in FIG. 1) and second lift mechanism 22 then liftstube 16 from table 21 (while first lift mechanism 17 is simultaneouslylifting another tube 16 from tub 15), transfers it forwardly tohydroforming station III, and places it into a hydroform tub generallyindicated at 24. Shuttle 14 then translates back to its idle position.In tub 24, preformed tube 16 is formed into frame member 25. Shuttle 14then translates to its rearward position where third lift mechanism 23lifts finally formed frame member 25 from tub 24, transfers it forwardlyto end cropping and ejection station IV, and releases it there where theends 29 are cropped to form the finished frame member 30.

Station I

Referring to FIGS. 3 and 4, blank feeder and burnishing station I willnow be described. Station I generally includes a hopper 12 with a pairof agitators 32, a ramp 13 with tube blow-out device 33, and a pair ofburnishing units 50. Ramp 13 includes a pair of opposed, parallel, anddeclining runners 36 which form, at their rear, the floor 35 of hopper12. Runners 36 are supported at the rear by opposed and vertical rearframe members 39 of hopper support frame 40 and at the front by rampsupport frame 41. Hopper framing and walls 42 extend rigidly forwardlyfrom rear frame members 39. A pair of opposed and parallel front guidemembers 37 are rigidly held by walls 42 to form a 90° angle with floor35 in order to receive a square bundle 38 of tube blanks 11. Althoughthe present invention may be adapted to operate with a variety ofdifferent tubular blanks, in the preferred embodiment, blanks 11 arewelded steel tubes made from cold rolled steel, deep drawing quality,special killed, having an outside diameter of 21/2 inches plus or minusone one-thousandth of an inch, and having a length of approximately 126inches. The welds of the tubes are planished to provide a smooth,reliable, and constant outside diameter. Guide members 37 are sized anddisposed so that the bottom end of each guide member 37 is spacedslightly more than 21/2 inches above its respective runner 36, thuscreating a pair of opposed escapements 43 through which tube blanks 11may roll, one at a time, out of hopper 12 and down ramp 13.

A pair of identical agitators 32 are opposedly mounted to the inside ofrespective runners 36 and rearwardly of escapements 43. Each agitator 32has a hydraulic drive cylinder 45 with a vertically extending piston rod46 which vertically reciprocates a corresponding agitator rod 47.Interposed between agitators 32 and their hydraulic pressure source (notshown) is a flow divider (not shown) to ensure simultaneous andcoinciding, reciprocating agitation. The up and down motion of agitatorrods 47 provide appropriate agitation to ensure a constant and smoothflow of blanks from hopper 12, through escapements 43 and onto ramp 13.

Angle iron guides 48 are rigidly mounted as by welding to the outside ofeach runner 36. Each guide 48 extends upwardly from its runner 36, theninwardly to hold blanks 11 vertically and laterally in place on ramp 13.

Referring to FIGS. 3, 4 and 5, a pair of triangular-shaped stops 49 arefixedly secured to the forward ends of runners 36. A pair of opposed,identical and aligned burnishing units 50 are also mounted at theforward end of ramp 13, to a corresponding runner 36, and slightlybehind stops 49. Each burnishing unit 50 includes a housing 55, aburnishing tool hydraulic drive cylinder 53, a tube blank hydraulicpush-up cylinder 54, and a low pressure tube blank hydraulic push-downcylinder 58. Tube blanks 11 roll freely, side-by-side, down ramp 13until the forwardmost blank 11 encounters stops 49. Push-up cylinders 54and push-down cylinders 58 are positioned so that the axes of upwardlyextending piston rods 56 of cylinders 54 and of downwardly extendingpiston rods 57 of cylinders 58 roughly intersect the axis of theforwardmost tube blank 11 which rests against stop 49. Upon actuation oflow pressure, push-down cylinders 58, piston rods 57 extend downwardlyagainst the corresponding blank 11. Actuation of push-up cylinders 54quickly extends piston rods 56 upwardly against the bottom of thecorresponding blank 11. Cylinders 54 are adapted to lift the blank 11,against the downward force of piston rods 57, up into alignment withburnishing units 50. While pressure is maintained in cylinders 54 and58, blank 11 remains firmly clamped between piston rods 56 and 57 forthe burnishing operation. The placement of drive cylinders 53, ofcylinders 54 and 58 and of stops 49 is such that when a tube blank isfirmly clamped between piston rods 56 and 57, the common axis 71 oftools 61 substantially coincides with the axis of the clamped tubeblank. Cylinders 54 and 58 are spaced inwardly from the tube blank endsto provide clearance for the inward extension of the burnishing tool.Interposed between the two push-up cylinders 54 and their hydraulicpressure source (not shown) is a flow divider (not shown) to ensure thesimultaneous and coinciding actuation of cylinders 54. A flow divider islikewise connected between push-down cylinders 58 and their pressuresource.

During production of the tube blanks 11, the outside diameter isreliable to within about plus or minus one one-thousandths of an inch.However, during the production process, a small, inwardly extendingdimple and an outwardly extending burr may be created at the end of theblank when the tube is cut to length. The outer ends of each tube blank11 are therefore burnished. Referring to FIGS. 4 and 6, the burnishingoperation of units 50 is performed by a burnishing tool 61 which isdriven by a pair of identical, reciprocating and hydraulic tool drivecylinders 53. Each cylinder 53 has a piston rod 60 extending inwardlytherefrom. Burnishing tool 61 is fixedly mounted to the end of pistonrod 60 in an appropriate manner. Tool 61 includes an inner, pilotportion 63 and an outer, cylindrical portion 64. Outer portion 64fixedly holds a cylindrical carbide bit 65, the interior surface 66 ofwhich defines the desired outer diameter of the end 62 of tube blank 11.Cylindrical portion 64 and bit 65 together define a tapering lead 72.Pilot portion 63 defines a tapering lead diameter section 68, asubstantially constant diameter section 69, and a chamfering diametersection 70. After a tube blank 11 is firmly clamped between piston rods56 and 57 and is substantially aligned with axis 71, drive cylinders 53are activated (by a hydraulic pressure source with a flow divider (notshown) interposed between the pressure source and cylinders 53 to ensuresimultaneous actuation of both cylinders 53), shooting tools 61inwardly. Tapering lead 72 opens outwardly enough to allow for slightmisalignment between tools 61 and the ends 62. Bit 65 then passes overand around end 62, simply shaving off any outer surface metal or burr tothe extent the outer diameter of end 62 is greater than the innerdiameter of bit 65. As bit 65 passes around end 62, lead diametersection 68 enters end 62, followed by entry of constant diameter section69, which pushes out any irregularities or dimples which might exist onthe inside surface of end 62. At the end of the burnishing stroke, acurved surface 74 defined in bit 65 and the chamfering section 70 impactupon end 62 to form a radiused outer edge 75 and a lead-in inner edge76, respectively. Tools 61 are then simultaneously retracted, leavingends 62 with the desired outer diameter and shape. The axial length oftool 61 and bit 65 may vary depending upon the axial length of blank end62 which is required to have a smooth and reliable diameter by thestructure of sealing units 95 and 201 of stations II and III.

Referring to FIGS. 3 and 5, after tools 61 have been retracted, push-upcylinders 54 are retracted, somewhat slowly at first, whereupon theworkpiece, blank 11, is unclamped and rolls forwardly off of piston rods56, down the ramped sides of stops 49 and into tub 15 of tangent bendand prehydroforming station II.

Rearwardly of burnishing units 50, angle irons 48 define a pair ofaligned holes at 77 and 78 which are spaced rearwardly of stops 49 so asto be aligned with the nth (6th in FIGS. 3-5) tube blank 79 back fromstop 49. While the forwardmost tube blank 11 is being burnished, a highpressure air blast is delivered via air line 80, through hole 77 andinto tube blank 79. Any loose dirt or debris is thereby blown out oftube blank 79 and through the opposing, aligned hole 78. A baffle 81 isprovided at hole 78 to deflect the exiting airstream downward. Anappropriate collection or filter device may be attached to baffle 81 tocontain the dirt and debris.

As shown in FIGS. 3, 10 and 11, the forming operation of Station II isperformed completely submerged in an aqueous bath 84 within tub 15.Appropriate means are provided to receive, guide and support blank 11which has just been ejected from burnishing units 50 and has rolled intoposition at 86 in aqueous bath 84. A limit switch 85 (FIG. 7) is alsoprovided which signals the receipt and proper placement of a blank 11 inthe ready position 86.

Station II

Referring now to FIGS. 7-12, there is shown one-half of tangent bend andprehydroforming station II. The machine elements of station II aregenerally symmetrical about centerline 18 and the following descriptionwill be made with regard to just one-half of station II as shown in FIG.7 (and FIGS. 9-11, as indicated).

Station II generally includes a tub 15 having a base 88 and walls 89which hold an aqueous bath 84 (FIGS. 1, 10 and 11). Bath 84 comprises ahigh water base fluid such as Hydro-Lube 120-B, commercially availablefrom Howghton Co. Referring to FIG. 7, tub 15 supports and contains awing 90, a die block 91, an inner die 92 and a wedge 93, all of whichlie substantially submerged in aqueous bath 84. Wing 90 is mounted topivot about a post 94 and its axis 103 between an opened position (shownin solid lines) and a closed position (shown in phantom). Wing 90carries a tube sealing unit 95, an outer die 96, and a tangent bendwiper shoe 97.

Sealing unit 95 has a saddle plate 100 which is mounted by saddle platepivot pin 101 to pivot about vertical axis 111. A hydraulic cylinderassembly 98 is fixedly mounted to saddle plate 100 by brackets 105 andhas an outwardly extending piston rod which defines at its outer end asealing tool 99. The solid-lined sealing unit 95 shows sealing tool 99fully retracted while the phantom lined sealing unit 95 shows sealingtool 99 fully extended. Hydraulic pressure is supplied to cylinder 98 atport 177 by a conventional hydraulic line (not shown).

Referring for a moment to FIG. 12, sealing tool 99 is shown fullyextended and engaged with the end 170 of a blank 11. Tool 99 defines anaxial bore 172. At the leading edge 173 of tool 99, bore 172 iscounterbored forming a chamfer 174. An o-ring 175 is seated within anannular cavity in bore 172, just inside from leading edge 173. Hydraulicport 177 extends through the wall at the top of tool 99. Conventionalpumping means (not shown) are provided to deliver the solution ofhydraulic bath 84, under pressure, to port 177. The means includes aconventional relief valve (not shown) which is set to a desired reliefpressure is described herein. The diameter of bore 172 is about thirtythousandths of an inch larger in diameter at 178 (slightly exaggeratedin FIG. 12 for description), inside of a line 179 located between o-ring175 and relief port 177, thus providing free fluid communication betweenthe inside of blank 11 and port 177.

Referring back to FIG. 7, outer die 96 is supported at opposite sidesfor sliding movement between a retracted position (FIG. 7) and anextended position (FIG. 9) by a pair of gibs 106. Gibs 106 each definean inwardly extending, overhanging flange 102 which mates with acorresponding outwardly extending, bottom flange 104 of die 96 to holddie 96 for lateral sliding movement atop wing 90. Gibs 106 are heeledand screwed (not shown) to wing 90. Die 96 is reciprocated between theretracted and extended positions by hydraulic cylinder assembly 107.Cylinder assembly 107 is mounted to die 96 by brackets 108. The outerend of piston rod 109 of assembly 107 is fixed to wing 90 by appropriatemeans such as a bracket 110 fixed to wing 90 and a bolt 112 whichextends through bracket 110 and is fixed into the end of piston rod 109.With piston rod 109 secured to wing 90 via bracket 110, extension andretraction of piston rod 109 causes die 96 to slide laterally betweenits extended and retracted positions. The right side 113 of die 96, asshown in FIG. 7, is contoured and defines a mold cavity 114 whichgenerally defines the desired plan view shape of a finally formed framemember. As seen in FIG. 8, mold cavity 114 of the present embodiment hasa semicircular cross-section matching that of tubular blank 11. Thecross-section of cavity 114, or of any of the subsequently describedcavities, may of course be defined in a variety of shapes to form thedesired plan view shape (both overall and in cross-section) of preformedtube 16 during the operation of station II.

Tangent bend wiper shoe 97 rests atop wing 90 between post 94 and anchorblock 115. Referring now to both FIGS. 7 and 10, shoe 97 is shown havingan inwardly extending lower portion 118. Lower portion 118 defines gearteeth 119 which are in constant meshing engagement with fixed pinion120. Pinion 120 is keyed in a fixed position to a block 116 which iskeyed and heeled to die block 91. Abutting the back edge 121 of shoe 97is a bronze wear plate 122 which is heeled in a complementary slot inanchor block 115 and against which shoe 97 slides as wing 90 rotates. Anupper bronze wear plate 124 overlaps shoe 97 and is appropriatelysecured atop anchor block 115 to hold shoe 97 vertically in place. Theinside side 123 of shoe 97 defines a semicylindrical mold cavity 125with a radius equal to the outer radius of tube blank 11.

Referring now to FIGS. 7 and 11, a die block anchor post. 126 extendsupwardly from tube base 88. Die block 91 rests atop a riser portion 128of base 88 and is keyed to post 126 against lateral movement. Die block91, like shoe 97, defines a semicylindrical mold cavity 131 with aradius equal to the outer radius of tube blank 11.

Referring to FIGS. 7, 9, 10 and 11, wedge 93 rests atop and is T-keyedat 127 to a riser portion 128 of tub 88 to slidably reciprocate alongcenterline 18. Key 127 is both heeled and screwed (not shown) into thebottom of wedge 93. A hydraulic cylinder assembly 129 is fixedly mountedto tub base 88. The outwardly extending end of piston rod 130 ofassembly 129 is appropriately fixed to wedge 93. Extension andretraction of piston rod 130 thus moves wedge 93 along centerline 18between a retracted position (FIG. 7) and an extended position (FIGS. 9,10 and 11). The end 137 of wedge 93, opposite piston rod 130 and likedie block 91, defines a semicylindrical mold cavity 138 with a radiusequal to the outer radius of tube blank 11.

Inner die 92 defines a contoured outer side 132 which defines a moldcavity 133. Like mold cavity 114 of outer die 96, side 132 defines asemicircular cross-section which is in the shape of the correspondingportion of the desired finally formed frame member. Like wedge 93, innerdie 92 rests atop and is keyed to riser portions (not shown) to slidablyreciprocate in the direction of arrows 134 between a retracted position(FIG. 7) and an extended position (FIGS. 9, 10 and 11). Die 92 is causedto reciprocate between its extended and retracted positions solely bythe camming action between T-key 135 of wedge 93 and T-key slot 136 ofdie 92 as wedge 93 is reciprocated between its retracted and extendedpositions by cylinder assembly 129. T-key 135 is heeled and screwed (notshown) to the side of wedge 93.

Mounted below tub base 88 is the drive assembly 140 which reciprocateswing 90 between its open and closed positions. Drive assembly 140includes a hydraulic cylinder assembly 141 secured to the underside ofbase 88. The outer end of piston rod 142 of assembly 141 is secured inan appropriate manner to a drive beam 143 which is supported and guidedby T-key 144 to slide along centerline 18. T-key 144 is heeled andscrewed (not shown) to the bottom of base 88. A rack 145 is heeled andkeyed (not shown) to beam 143 and has gear teeth at 146 which mesh witha pinion 147. A circular retainer plate 150 is bolted by screws 151 tothe bottom of post 94, trapping coaxial pinion 147 between plate 150 andbase 88. Plate 150 defines an annular shoulder 152 within which isseated a bronze wear ring 153. Rack 145 slides atop wear ring 153 asrack 145 meshes with and rotates pinion 147.

The top of post 94 defines a reduced diameter portion 155, about whichis seated a coaxial, bronze wear bushing 156 and coaxial pinion 120.Pinion 120 is supported atop wing 90, but is keyed in a fixed,non-rotating position by block 116 (FIG. 7). Wear bushing 156 has acylindrical portion and an upper, outwardly extending, annular flangeportion seated in a complementary annular shoulder in pinion 120.Together, bushing 156 and pinion 120 define an annular shoulder 157within which is seated a circular retaining cap 154. Cap 154 is screwedto reduced diameter portion 155 by screws 158. Post 94 is primarilysupported by wing 90 via keys 165. Cap 154 via that portion of cap 154which is seated in shoulder 157 provides insurance to support post 94,retaining plate 150, ring 153 and pinion 147 in the event that keys 165should loosen. Post 94 extends through a complementary opening 162defined in base 88 with a coaxial, cylindrical bronze bushing 163interposed therebetween. A pair of spaced o-rings 164 are disposedwithin appropriate annular grooves in post 94 to seal against leakagefrom tub 15. Wing 90 is keyed to rotate as a unit with post 94 by keys165. Finally, tub 15 is filled with aqueous bath 84 to a level 167 wellabove the semicircular cross-sectioned cavities 114, 125, 131, 133 and138 of outer die 96, shoe 97, die block 91, inner die 92 and wedge 93,respectively. Preferably, the fluid level 167 is maintained roughly ator above the top of dies 92 and 96, as shown in FIGS. 10 and 11.

It should be noted that the centerlines of each cavity (line 167 ofcavities 125 and 133, FIG. 10, and line 168 of cavities 131 and 138,FIG. 11, for example) all lie in the same plane. In other words, theforming operation of station II occurs exclusively by the horizontallyapplied pressure of wiper shoe 97, dies 92 and 96, wedge 93 and dieblock 91.

Referring to FIGS. 7-12, the operation of tangent bending andprehydroforming station II is as follows:

At the end of the burnishing operation of station I, when tube blank 11is released by push-up cylinder 54, the components of station II are asthey appear in FIG. 7: wing 90 is in the open position and outer die 96,inner die 92 and sealing cylinder tool 99 are all retracted. Uponrelease from push-up cylinder 54, blank 11 rolls off stops 49 and intotub 15, sinking immediately into bath 84, below fluid level 167, andresting atop extended portion 118, pinion 120 and an appropriate blanksupport 83. Blank support 83 includes a limit switch 85 which verifiesthat blank 11 has been received in the appropriate ready position 86.With dies 92 and 96 retracted, blank 11 in ready position 86 restshorizontally aligned with cavities 114, 125, 131, 133 and 138 of outerdie 96, shoe 97, die block 91, inner die 92 and wedge 93, respectively.Limit switch 85, along with any other appropriate and desired sensorsdisposed throughout apparatus 10, send signals to a microprocessor (notshown) which governs the overall operation of machine 10.

After verification of the proper positionment of blank 11, cylinderassembly 129 extends wedge 93 along centerline 18, whereby inner die 92is translated along arrows 134 into its extended position, and wherebythe leftmost portion of cavity 133 (as shown in FIG. 7) contacts blank11 and moves it leftwards, into cavities 131 and 125 of die block 91 andshoe 97, respectively. Once wedge 93 and inner die 92 are fullyextended, cavity 138 and the leftmost portion of cavity 133 mate withopposing cavity 131 to completely encircle and firmly clamp the centrallength of blank 11 while cavity 125 of shoe 97 half-way encircles aneighboring length of blank 11. Blank 11 is now axially aligned withsealing tool 99 of sealing unit 95. Further, hollow tube blank 11 andsealing tool 99, being completely submerged within bath 84, are bothautomatically filled with the aqueous solution of bath 84.

Cylinder assembly 98 is now actuated whereby sealing tool 99 extends andtelescopically surrounds distal end 170 of blank 11. (FIG. 12)Counterbore 174 of tool 99 allows for possible minor misalignmentbetween distal end 170 and sealing tool 99 during engagement of tool 99.The radiused edge 75 of blank 11 reduces the risk of chafing to o-ring175 as tool 99 telescopically extends over end 170. As tools 99 (thereis an identical companion tool 99 simultaneously operating at the otherdistal end of blank 11 on the unshown half of station II) simultaneouslyextend onto the respective distal ends 170, o-rings completely seal theinterior of blank 11, and tools 99 become pistons, compressing andincreasing the pressure of the liquid within blank 11 and bores 178. Astools 99 extend through their full stroke, the pressure within blank 11and bores 178 is relieved via ports 177 and the relief valves connectedthereto (not shown) as necessary to maintain the desired internalpressure. The slightly larger diameter portion 178 of bore 172 inside ofline 179, as shown in FIG. 12, ensures an unobstructed flow of fluidfrom within blank 11 and out of port 177.

The pressure relief valves (not shown) connected to relief ports 177 areset at the value of desired pressure within blank 11, which, in thepresent embodiment, is just below the burst pressure of blank 11 whichis approximately 2880 p.s.i. The burst pressure is determinedapproximately by P_(burst) =(2×th×TS)/(2×r) where th=the wall thicknessof blank 11; TS=the tensile strength of blank 11; and, r=the insideradius of blank 11. Here TS=45,000 p.s.i.; th=0.08 inches; and, r=1.25inches.

Once sealing cylinder 99 is fully extended and surrounding distal end170, distal edge 176 of blank 11 will extend about 10 inches into bore172 as shown at position a (FIGS. 7, 9 and 12); tube blank 11 and bore172 will be filled with the aqueous solution of bath 166; and thepressure of the solution within blank 11 will be somewhat below theburst pressure of about 2880 p.s.i.

With the pressurized fluid within blank 11 forming a flexible mandrel,tangent bend cylinder assembly 141 is now actuated, extending drive beam143 and rack 145, and turning pinion 147, post 94 and wing 90. As wing90 rotates, wear plate 122 of block 115 revolves about post axis 103 andbears against shoe 97. Since pinion 120 is fixed against rotation, shoe97 is caused to tangentially roll about pinion 120 and, at the sametime, to tangentially bend tube blank 11 around cavity 133 of inner die92. By selecting the proper configuration, placement and dimensions ofshoe 97, block 115, pinion 120 and inner die 92, shoe 97, via its cavity125, primarily "wraps" rather than "slides" about blank 11. This causesthe inside portion (adjacent to cavity 133) of the 21/2 inch diametertube blank 11 to "wrap" and not wrinkle. Obviously, the balance of theblank must stretch to generate the desired form. In the presentembodiment, the pitch diameter of pinion 120 is four inches which placesthe intersection of the pitch circle of pinion 120 and of the pitch lineof the gear teeth of portion 118 approximately vertically aligned withthe innermost portion of mold cavity 133. This creates nearly perfecttangential bending at the innermost side of blank 11 (i.e., nostretching and no compressing). By replacing pinion 120 with a pinionhaving a larger pitch diameter and replacing shoe 97 with a narrowershoe (i.e., portion 118 with the gear teeth extends just far enough fromblock 115 to mesh with pinion 120) the intersection of the pitch circleof pitch line of geared pinion 120 and the extended portion 118 will bevertically between the inner and outer side of blank 11 thereby causingsome compression of the inner side and lessening the amount of stretchat the outer side.

At the end of its rotation, wing 90 has rotated 90° to its closedposition, and blank 11 has been bent 90° about inner die 92 (shown inphantom in FIG. 7). Sealing unit 95, pivotally mounted at pin 101, hasfollowed and remained coaxial with end 170 of blank 11. The bending hascaused distal end 170 to telescopically retract about 2 inches fromwithin sealing tool 99 (indicated as position b in FIGS. 7 and 9), butseal 175 (along with hydraulic pressure source connected at port 177)has maintained the desired less-than-burst pressure within blank 11.

A piston actuated locking block 187 is next extended to lodge adjacentto and between the end of wing 90 and a back-up block 188 which is fixedto tube base 88 (shown in solid lines in an unlocked position in FIG.7). Before cylinder assembly 107 is actuated, block 187 is extended to alocking position (FIG. 9).

With inner die 92 still extended (as shown in FIG. 9), cylinder assembly107 is next actuated, extending outer die 96 toward inner die 92 andagainst blank 11. As die 96 approaches and finally mates with inner die92, straight, tangent bent leg 180 of blank 11 is prehydroformed into aleg 183 having the desired plan view configuration defined by themutually cooperating cavities 114 and 133. The vertical axis 111 ofpivot pin 101 is located at the intersection of axis 181 (of tangentbent leg 180) and axis 184 (the axis of distal end 170 after the formingoperation of dies 92 and 96). Sealing tool 99 thus pivots about axis 111during the prehydroforming operation, and maintains a seal on distal end170. At the end of the prehydroforming operation by dies 92 and 96,distal end 170 retracts another three inches from within sealing tool 99(indicated as position c in FIG. 9).

Block 187 is retracted to the unlocked position, sealing tool 99 isretracted, wing 90 is pivoted to the open position, and dies 92 and 96are retracted, thereby releasing preformed tube 16. Shuttle 14 thentranslates to its rearward position where first lift mechanism 17 ramsdown, clamps shaped tube 16, and rams up with tube 16. Shuttle 14 thentranslates to its forward position where mechanism 17, now at idlestation 20, rams down and releases tube 16, placing it onto table 20.Mechanism 17 rams up and shuttle 14 translates back to the idleposition. Appropriate means are provided for pivoting sealing unit 95,upon opening of wing 90, back to its starting position (as shown in FIG.7) to engage with the next tube blank 11.

Station III

Referring to FIG. 13, there is shown an end view of hydroforming stationIII wherein a preformed tube 16 is formed within a specialstuffing-ledge arrangement in a die 195 and a punch 196. Station IIIgenerally includes a variable ram speed hydraulic press 186 having apair of overhead hydraulic cylinder assemblies 189 which verticallyreciprocate a punch 196. A tub 190 having a base 191 and walls 192 issupported upon a press bed 194. Tub 190 is filled to an appropriatelevel with the same aqueous bath which is contained in tub 15 of stationII. Punch 196, as shown in FIG. 13, is in a fully retracted position.

Referring to FIGS. 14-16 and 18, die 195 includes a central post portion202 which defines an outwardly facing, contoured, and vertical, punchengaging wall 203. The base of wall 203 smoothly transitions intoupwardly facing ledge 199 which defines the bottom half of the partprint of a finally formed frame member 25. Below and outwardly fromledge 199, die 195 defines an outwardly facing, contoured, and verticalheel 204.

Punch 196 defines a complementary, downwardly extending post portion 207which defines an inwardly facing, vertical, die engaging wall 208. Dieengaging wall 208 is contoured to telescopically engage with heel 204 insubstantially complete adjacent engagement. Wall 208, at its top,smoothly transitions into a downwardly facing ledge 210 which definesthe upper half of the part print of a finally formed frame member 25.Punch 196 further defines, inwardly from ledge 210, an inwardly facingand vertical heel 209. Heel 209 is contoured to telescopically engagewith outwardly facing, punch engaging wall 203 in substantially completeadjacent engagement. That is, as punch 196 rams vertically downward,ledge 210 is in constant alignment above ledge 199, vertical heel 209slides along vertical wall 203, and vertical wall 208 slides alongvertical heel 204. The plan view of both ledges 199 and 210 issubstantially identical to the plan view of preformed tube 16 as formedin tangent bend and prehydroforming station II. As shown in FIG. 18, thelower portion of punch engaging wall 203 smoothly transitions into ledge199. The transition between ledge 199 and heel 204, on the other hand,forms a severely acute angle as seen at 211. The intersection betweenledge 199 and heel 204, along its entire length, is radiused off at 212with a radius of approximately 3/8ths of an inch. This radius may varydepending on the characteristics of the tube being formed and the forcesto which it is to be subjected. In the present embodiment, a 3/8ths inchradiusing at 212 is too small to result in outward deformation of tube16 into the gap 205 created between radiused edge 212 and wall 208during the below-described step of boosting the internal pressure withintube 16. This is because the boosted pressure applied to the interior oftube 16 is insufficient to cause deformation of the walls of tube 16into an area the size of gap 205. The transitions between die engagingwall 208 and ledge 210 and between ledge 210 and heel 209 of punch 196are similarly sized.

As evidenced by the elevational view of finally formed frame member 25in FIG. 1, ledges 199 and 210, in the present embodiment, both varyvertically over their length. The central sections (213 and 214) of bothledges 199 and 210 project downwardly. Thus, as seen in FIGS. 15 and 16,when preformed tube 16, having a horizontally straight profile, is laidupon die 195, surrounding central post 202, tube 16 will contact ledge199 only at the front and rear portions. When punch 196 is rammed down,toward die 195, only the central, downwardly projecting portions 214 ofledge 210 will first contact tube 16. Further downward movement of punch196 will of course begin to bend tube 16 between ledges 199 and 210.

Vertical movement of the punch 196 is controlled by transducers whichgovern the operation of cylinder assemblies 189. Four stop blocks 206are mounted to base 191 of tub 190 and are sized to be hit by the bottomof punch 196, thereby defining the lower limit of its stroke. At itslower limit, punch 196 is fully extended and engaged with die 195. Aclosed cavity is thereby defined between ledges 199 and 210 which cavityis the part print of finally formed frame member 25. In the presentembodiment, the cross-sectional configuration of the closed cavityformed between ledges 199 and 210 varies considerably along the entirelength thereof. At some points along that length, the perimeter of thecross-section defined by the closed cavity is larger than the perimeterof the corresponding cross-section of the preformed tube 16 which is tobe placed and formed therein.

Sealing units 201 are mutually identical and are similar in nature tothe sealing units 95 of station II. Each sealing unit includes ahydraulic cylinder assembly 217 having an outwardly extending piston rod216 with a sealing tool 218 rigidly connected at the end thereof. Tool218 defines a bore 219 within which is seated an o-ring 220 a shortdistance back from leading edge 221. Bore 219 is counterbored to form alead-in 215 to allow for any misalignment between end 170 and bore 219.Each tool 218 is mounted for reciprocal sliding movement by gibs 233along the corresponding common axis 236 of piston rod 216 and of end 170of tube 16 as initially placed upon die 195. Each tool 218 defines apair of outwardly extending flanges 234 which extend into mating slots236 in gibs 233. Gibs 233 are appropriately mounted to tub base 191.Unlike sealing unit 95 of station II, hydraulic ports 222 are defined incorresponding tools 218 so as to never be located over any portion oftube 16 when tool 218 is fully extended and engaged with tube end 170.

Central post portion 202 of die 195 defines a central cavity 224 withinwhich is mounted hydraulic pressure intensifier 225. Intensifier 225generally includes a first hydraulic cylinder 226 with a piston 228.Cylinder 226 is driven by an appropriate hydraulic pressure source (notshown), via ports 231 and 232, and uses oil as the driving fluid.Reciprocation of piston 228 causes its piston rod 229 to reciprocatewithin separate cylinder 227, the end face 230 of piston rod 229 forminga piston within cylinder 227. In the present embodiment, the effectivecross-sectional area of piston 228 is roughly four times greater thanthe effective cross-sectional area of piston face 230, resulting in apressure increase from cylinder 226 to cylinder 227 of about 4-to-1.Connected to each port 222 is a low-pressure relief valve (not shown)which is set at the just-less-than burst pressure (about 2880 p.s.i.).The low pressure relief valve vents excess pressure from bores 219 backinto the aqueous bath 193 as is described herein. Inlet/outlet port 240of cylinder 227 is also connected to both ports 222, and independent ofthe low-pressure relief valve. Appropriate switching mechanisms areprovided relative to ports 222, port 240 and the low pressure reliefvalve to provide the desired hydraulic operation as described herein. Ahigh pressure relief valve (not shown) is also provided at port 240 tolimit the pressure applied from cylinder 227 to bores 219 to the desiredboosted pressure (about 9600 p.s.i.).

Operation of the hydroforming apparatus of station III is as follows:

With punch 196 in the upwardly retracted position (as shown in FIG. 13and indicated at 198 in FIG. 15) and tools 218 fully retracted, secondlift mechanism 22 transfers a preformed tube 16 from idle station 20 tohydroforming station III and places it onto ledge 199. Lift mechanism 22then releases tube 16 and retracts and shuttle 14 returns to its idleposition. As soon as lift mechanism 22 clears the path 238 of punch 196,punch 196 quickly rams down to a tube trapping position (FIGS. 15, 16and 18). At this position, downwardly projecting, central section 214 ofledge 210 is just above tube 16. Also, downwardly extending post portion207 has substantially surrounded tube 16 and a portion of die 195. Atthis point, the bottom edge 239 of die engaging wall 208 has passedbelow the radiused edge 212 of ledge 199 at its lowest point (213). Iftube 16 was not completely vertically aligned with ledge 199--i.e.,sprung slightly outwardly--, post portion 207 of punch 196 will cam tube16 inwardly to its proper, vertically aligned position. Further, tub 190is filled with the aqueous bath 193 to a level 200 which is well abovetools 218 and above the top of tube 16 as placed upon die 195. Uponplacement of tube 16 into tub 190 and onto die 195, tube 16 is thusautomatically filled with the solution of aqueous bath 193. Tube 16 isnow completely trapped within a stuffing ledge cavity defined by ledges199 and 210 and vertical walls 203 and 208; and tube 16 and bores 219 oftools 218 are entirely filled with the solution of bath 193. Punch 196now dwells momentarily while sealing tools 218 simultaneously,telescopically extend around now aligned ends 170 of tube 16. Likeo-rings 175 of sealing units 95 of station II, o-rings 220 of sealingunits 201 are capable of maintaining a seal for the approximately 2880p.s.i. to be exerted within tube 16. As o-rings 220 extend and engageand seal ends 170, a closed volume is formed by tube 16 and bores 219except for ports 222. The low-pressure relief valves (not shown)connected at ports 222 relieve the excess hydraulic pressure in tube 16as tools 218 are further extended.

With tools 218 fully extended, with the internal hydraulic pressure oftube 16 roughly at the less-than-burst pressure, and with punch 196dwelling at the tube trapping position shown in FIGS. 15 and 16, punch196 rams down until it hits stop blocks 206. Punch 196 is now in itsfully extended position (not shown). As ledges 199 and 210 approachedeach other, tube 16 was still completely trapped within the stuffingledge cavity defined by ledges 199 and 210 and vertical walls 203 and208. Tube 16 had nowhere to escape or to be pinched. Instead, tube 16merely conformed to the shrinking, contoured cavity which, upon completeextension of punch 196, was defined entirely by walls 203 and 208 andledges 199 and 210. The flexible mandrel of tube 16 created by theinternal hydraulic pressure ensures uniform, non-buckling deformation oftube 16 according to the shape of ledges 199 and 210.

After punch 196 has been completely extended, preformed tube 16 has beenformed into finally formed frame member 25, except in those areas wherethe cross-sectional perimeter of the mutually cooperating ledges 199 and210 is greater than the corresponding cross-sectional perimeter of tube16. To complete the forming process as to these areas after punch 196has been fully extended, punch 196 dwells while intensifier 225 isactivated. An appropriate hydraulic valve isolates the path from port240, through the high-pressure relief valve (not shown) and to ports222. Actuation of intensifier 225 provides a pressure in excess of 9600p.s.i. at port 240, and, with the high pressure relief valve seriallyconnected between port 240 and ports 222, no more than the desired 9600p.s.i. is applied to the interior of tube 16. Being well above the burstpressure of tube 16, tube 16 expands to conform to the cavity defined bymutually cooperating ledges 199 and 210. The desired boosted pressure(P_(boost)) of 9600 p.s.i. of the present embodiment is determined bywhatever minimum radius (r) is defined in cross-section of the finallyformed frame member and is given approximately by P_(boost)=(2×th×TS)/(2×r) where th=the wall thickness of tube 16 and TS=thetensile strength of tube 16.

It is also noted that seal 220 need not be able to withstand the 9600p.s.i. boost pressure. At some point above the burst pressure (about2880 p.s.i.) tube 16 will expand between seal 220 and leading edge 221of tool 218, several thousandths of an inch until contacting andcreating a mechanical seal thereat with tool 218. After completion ofthe pressure boosting, cylinder 226 is reversed, retracting piston 229and relieving the boosted pressure within tube 16. Appropriate valvemeans (not shown) then vent the remaining pressure in tube 16 to bath193. The inherent springback in the metal will cause a reduction of theoutside diameter of end 170, thereby breaking the mechanical seal andallowing tool 218 to retract from end 170 uninhibited. Tools 218 arethen retracted, and die 196 is rammed up to its retracted position.Shuttle 14 translates from its idle position (where lift mechanism 23rests midway between stations III and IV) to its rearward position(where lift mechanism 23 is positioned over station III). Lift mechanism23 then rams down, clamps finally formed frame member 25 and rams up,lifting it out of tub 190. Shuttle 14 then translates to its forwardposition (where lift mechanism 23 is positioned over end cropping andejection station IV). Lift mechanism 23 releases frame member 25 wherethe unformed ends 29 (about 10 inches each on each end 170) of framemember 25 are cut off, forming the finished frame member 30 which isdelivered to an appropriate receiving area.

Transfer System

Referring now to FIGS. 1, 2, 13 and 17, transfer system 19 of thepresent invention is symmetrical about the vertical plane 244 (throughwhich centerline 18 passes). Generally, transfer system 19 includesthree pairs of opposed lift mechanisms 17, 22 and 23. Lift mechanisms17, 22 and 23 are mounted on parallel and opposing traveling beams 245.Beams 245 are rigidly connected by a pair of cross members 246 to form arigid, horizontally reciprocating shuttle 14. A shuttle bed 247 isrigidly mounted to the bottom of each transfer beam 245. Shuttle bed 247extends outwardly from beam 245 along the length thereof to define apair of longitudinal tracks 248 which ride within three groups (rear251, middle 252 and front 253) of three sets of rollers (top 255, middle256 and bottom 257). In each roller group 251, 252 and 253, top andbottom rollers 255 and 257 are held to rotate about a horizontal axisand middle rollers 256 are held to rotate about a vertical axis by apair of roller mounting brackets 258 which are supported by transfer bed259. Brackets 258, rollers 255, 256 and 257 and shuttle bed 245 are allsized and arranged so that longitudinal tracks 248 rest and ride atopbottom rollers 257 in each group 251, 252 and 253; so that the outeredges of tracks 248 are in constant contact with and thereby kept inhorizontal alignment by middle rollers 256 of all three groups 251, 252and 253; and, tracks 248 are in constant contact with and are therebykept vertically aligned by top rollers 257 of all three groups 251, 252and 253. Shuttle 14 is horizontally translated by a shuttle drivecylinder 262 which is mounted to transfer bed 259. The piston of drivecylinder 262 is connected to shuttle bed 247 by a bracket 267.

Each lift mechanism 17, 22 and 23 is supported by a cantilevered supportbeam 260 which in turn is rigidly mounted to traveling beam 245. Thelift mechanism 23 shown in FIG. 17 (which is representative of liftmechanisms 17 and 22) includes a transfer fixture 263 supported forvertically reciprocating movement by the piston rod 264 of a hydrauliccylinder assembly 265 which is mounted to support beam 260. A pair ofguide rods 266 are fixed to fixture 263 and extend upwardly throughcomplementary slots in support beam 260 to keep transfer fixture 263 inhorizontal and rotational alignment. Transfer fixture 263 includes ahydraulic clamping cylinder assembly 269, the piston rod of whichdefines a clamping arm 270. Fixture 263 also defines an upper clampingsurface 271.

To clamp a tube 16, for example when lift mechanism 23 is properlypositioned over tub 190 of station III, cylinder assemblies 265simultaneously lower their transfer fixtures downward until upperclamping surface 271 is just above or just touches the top of the tube16. Clamping cylinder assemblies 269 simultaneously extend theirclamping arms 270 inwardly, thereby camming tube 16 upwardly into aclamping arrangement between the opposing fixtures 263 and betweenclamping arm 270 and upper surface 271. Cylinders 265 thensimultaneously raise their fixtures 263, and shuttle 14 is translated asdesired to carry tube 16 to a desired position.

Lift mechanisms 17, 22 and 23, and traveling beams 245 and roller groups251, 252 and 253 are sized and positioned so that when shuttle is in arearward position (FIG. 1), lift mechanism is appropriately positionedover the work piece at station II, lift mechanism 22 is appropriatelypositioned over table 21, and lift mechanism 23 is appropriatelypositioned over the work piece at station III, and so that shuttle 14may be translated to a forward position (not shown) whereby liftmechanism 17 occupies the position previously occupied by lift mechanism22 over table 21, lift mechanism 22 occupies the position previouslyoccupied by lift mechanism 23 of station III, and lift mechanism 23 isappropriately positioned at station IV. The idle position of transfersystem 19 is defined by shuttle 14 being midway between the rearward andforward positions whereby lift mechanisms 22 and 23 rest on either sideof press 186 in order to be clear from the path of verticallyreciprocating die 196.

The period for one complete cycle of the present invention is defined bythe elapsed time during which: shuttle 14 moves from its idle positionto its rearward position; the transfer fixtures 263 of lift mechanisms17, 22 and 23 drop, clamp their respective work piece and rise with thatwork piece; shuttle 14 translates to its forward position; transferfixtures 263 drop, unclamp their respective work pieces and then riseback up; and, shuttle 14 returns to its idle position and rests untilthe various operations occur at stations I, II, III and IV, after whichshuttle 14 moves from its idle position to its rearward position,beginning a new cycle. It is estimated that the period for a singlecycle will be dictated by the hydroforming operation at station III andwill be 29 seconds.

Also included but not shown in the present invention are a variety ofsensors as appropriate to monitor the position and operation at eachstation. Flow dividers will be used in the hydraulic circuits whereverdesired to achieve simultaneous and coinciding operation of pairs ofcooperating cylinder assemblies. Proportional valves will also beemployed in the hydraulic circuit to achieve variable acceleration anddeceleration rates. Also, high resolution transducers will be used tocontrol the various die, fixture and shuttle operations to ensureprecision operation.

While the shape of the part formed in the present embodiment resulted ina punch and die configuration wherein the vertical walls 203 and 208,heels 204 and 209, and ledges 199 and 210 all had a particularorientation, it is noted that other orientations are possible and may,in fact be dictated by the part to be formed.

Referring to FIGS. 14-16 and the operation at station III, the completecross-sectional profile the finished frame member 30 may be formed froma preformed tube 16 by the stuffing ledge punch and die operationwithout the pressure boosting step. Where the part print of the desiredfinally formed frame member (as defined by mutually cooperating ledges199 and 210) has one or more cross-sectional perimeters along its lengthwhich are larger (5-10%, for example) than the correspondingcross-sectional perimeter of the tube 16 yet to be formed, the tube mustbe expanded at those points into the desired form by boosting theinternal hydraulic pressure. While this procedure may now be reliablyand quickly performed by the present invention, another significanttube-forming operation may be performed by the same components of thepresent invention. Instead of requiring the application of high internalpressure to expand the tube into small radiused corners, the stuffingledge and hydroforming arrangement of the present invention will form acircular cross-sectioned tube into a finally formed frame member havingsharp corners during the application of the less-than-burst (about 2880p.s.i.) internal pressure. This may be achieved where thecross-sectional perimeter of the finally formed frame member isapproximately equal to that of the blank to be formed. In the stuffingledge arrangement of station III, there are no openings between mutuallycooperating die halves during the final, critical moments of tubecompression within which the tube may "pinch." With the existence of theless-than-burst internal pressure, and where the cross-sectionalperimeter of the stuffing ledge cavity is approximately equal to thecross-sectional perimeter of the tube to be formed, I have discoveredthat the tube will form into sharp corners of the stuffing ledgeswithout the necessity of applying the high internal pressure (9600p.s.i.). This discovery is significant because it obviates the need toprovide an excessively high downward force upon punch 196 by cylinderassemblies 189 (i.e., about 15 tons) to keep punch 196 vertically inplace during the 9600 p.s.i. pressure boost.

It should also be noted that walls 203 and 208 and heels 204 and 209 arevertical and that punch 196 is adapted, therefore, for verticalreciprocation. It is to be understood that non-vertical applications arealso contemplated by the present invention so long as walls 203 and 208and heels 204 and 209 and the motion of punch 196 are all in parallelplanes.

In an alternative embodiment, hydraulic accumulators may be connected toports 177 of sealing units 95 whereby, as sealing tools 99 extendinwardly and over ends 170 of tube 11, hydraulic pressure from ports 177energize a pair of corresponding accumulators. After sealing tools 99seal and pressurize tube 11 as previously described the stored hydraulicpressure in the accumulators is switched to feed ports 177, through anappropriate relief valve set at the desired pressure. Thus, during thetangent bend and prehydroforming operation, any pressure drop (due toleakage or increase in internal volume) will be replenished by theaccumulators.

Referring to FIGS. 19-20, an alternative embodiment is shown wherein theburnishing units 50 of blank feeder and burnishing station I and thesealing units 95 of tangent bend and prehydroforming station II arereplaced by a pair of combination burnishing and sealing units 280. Asthe two combination units 280 are identical, the following descriptionwill apply equally to both units. Like sealing unit 95 (FIG. 7),combination unit 280 is mounted atop the saddle plate 100 to pivot aboutvertical axis 111. Combination unit 280 generally includes afoot-mounted, double-end rod cylinder assembly 279 with a one-quarterinch fluid passage 288 extending from a fluid supply line 289 to acombination burnishing and sealing tool 286, mounted at the forward endof rod 285. Cylinder assembly 279 includes a forward head 281, a rearhead 282, a cylinder 283 mounted therebetween, a piston 284 and a pistonrod 285. Piston 284 is rigidly mounted to move as a unit with piston rod285. Forward and return ports 291 and 292 provide pressure to theforward and rear sides of piston 284 to reciprocate piston 285 andcombination tool 286.

Referring to FIG. 20, combination burnishing and sealing tool 286includes a pilot 294 having a central post portion 295. Acylindrically-shaped outer shell 296 coaxially surrounds post portion295 and is securely mounted to pilot 294 by appropriate screws 297. Bothpilot 294 and shell 296 are made of a A-2 tool steel having a Rockwellhardness of approximately 50. Post portion 295 defines an outwardlyfacing, cylindrical recess 299 within which is seated by shrink fit atungsten carbide, cylindrical, inner insert 300 having a Rockwellhardness of approximately 90. Outer shell 296 defines an inwardlyfacing, cylindrical recess 301 within which is seated by shrink fit acylindrical outer insert 302 having a Rockwell hardness of approximately90. Insert 300 along with post portion 295 and outer insert 302 alongwith shell 296 define sloping, annular entry surfaces 303 and 304,respectively. Entry surfaces 303 and 304 together define an annular,V-shaped groove to allow for any misallignment when combination tool 286is extended onto the end of blank 11.

Referring now to both FIGS. 20 and 21, the outer surface 305 of insert300 is ground to produce an outer diameter equal to the inner diameterof blank 11 minus 0.005 inches clearance. The inner surface 306 ofinsert 302 is ground to produce an inner diameter equal to the outerdiameter of blank 11 plus 0.005 inches clearance. With inserts 300 and302 and outer shell 296 and pilot 294 completely assembled, inner andouter surfaces 305 and 306 create a cylindrical groove or "gland" 308for sliding receipt of the end 170 of blank 11. Gland 308, incross-section as shown in FIG. 21, is symmetrical about a line ofsymmetry 307. Each of surfaces 305 and 306 is ground at its inner end atan angle a approximately equal to 2°. The innermost end 309 of gland 308thereby converges toward line of symmetry 307 at an angle ofapproximately 4°. In the present embodiment, the wall thickness of blank11 is approximately 0.08 inches and the distance along line of symmetry307 over which gland 308 tapers is approximately 0.8 inches.

Combination burnishing and sealing unit 280 operates in conjunction withtangent bend and prehydroforming station II as follows:

With blank 11 resting within bath 84, and firmly clamped by inner die92, die block 91 and shoe 97 as described above, blank 11 is axiallyaligned with combination burnishing and sealing tool 286. Further,combination tool 286, like sealing tool 99 of the previous embodiment,is completely submerged within the aqueous bath, and both tool 286 andblank 11 are thus automatically filled with the aqueous solution.Cylinder assembly 279 is now actuated by forcing fluid through forwardport 292, causing piston 284 and rod 285 to move to the left (in FIGS.19-21), whereby combination tool 286 extends and telescopicallysurrounds end 170 of blank 11. The V-shaped, annular groove defined bysloping surfaces 303 and 304 allows for possible misalignment betweendistal end 170 and tool 286. Near complete extension of piston rod 285and tool 286 will force distal end 170 of blank 11 through gland 308 andinto tapering end 309. As a result, the wall of distal end 170 will becompressed or coined. (The distal end 310 will form a V-cross-section,as shown in FIG. 21.) A substantially water-tight seal will be createdbetween end 170 and inserts 300 and 302 at the surfaces of contactwithin the converging end 309. With a Rockwell hardness of approximately90 and all of surfaces 305 and 306 ground smoothly, the coefficient offriction between inserts 300 and 302 and blank 11 is very low. This willallow blank 11 to slide smoothly out of gland 308 after completion ofthe hydroforming process.

Combination unit 280 is dimensioned so that upon initial sealing, piston284 is spaced a distance w from forward head 281. Distance w is thereserved forward stroke of piston 284 corresponding to the retraction ofdistal end 170 from within the particular sealing tool as a result ofthe prehydroforming operation as described and shown by positions a, band c in FIG. 9. In other words, piston 284 will not bottom out againsthead 281. Rather, pressure is always provided during hydroforming,through port 292 to keep combination tool 286 and gland 308 sealedagainst the end of blank 11.

As with sealing unit 95, conventional pumping means (not shown) areprovided to deliver aqueous solution, under pressure, to fluid supplyline 289. The pumping means also includes a conventional relief valve(not shown) which is set to a desired relief pressure as describedabove.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

What is claimed is:
 1. An apparatus for bending a tube blank having anouter diameter, comprising:an inner bending die having an arcuate outersurface which has a first radius from an axis; a wiper shoe having aninner surface, said shoe disposed and adapted to trap a tube blankbetween said inner surface and said outer surface; holding means forholding a first portion of the blank against said inner die; limitingmeans for limiting movement of said shoe to rolling about an arc aroundsaid axis, said arc having a second radius from said axis which isapproximately between said first radius and said first radius plus saiddiameter; and, moving means for moving said shoe around said axis, andaround the blank thereby bending a second portion of the blank aroundsaid outer surface; and sealing and pressurizing means for sealing theblank and for hydraulically pressurizing the interior of the blank to asufficient pressure to allow said moving means to bend said secondportion of the blank around said outer surface, said pressurized liquidacting like a flexible mandrel to alone ensure uniform, non-bucklingdeformation of the tube, substantially without distorting the crosssection of the second portion.
 2. The apparatus for bending a tube blankof claim 1 wherein said second radius is approximately equal to saidfirst radius.
 3. The apparatus for bending a tube blank of claim 1wherein said limiting means includes a stationary pinion coaxial withsaid axis and a rack rigidly connected to said shoe and tangentiallyengaged with said pinion.
 4. The apparatus for bending a tube blank ofclaim 3 wherein said inner and outer surfaces each define a mutuallycooperating mold cavity sized to completely enclose a portion of theblank.
 5. The apparatus for bending a tube blank of claim 1 wherein thetube blank has first and second opposing ends and wherein said sealingmeans includes a pair of tools having bores, said tools being adapted totelescopically extend over said ends to seal and pressurize the tubeblank.
 6. The apparatus for bending a tube blank of claim 1 furtherincluding filling means for automatically filling the tube blank withliquid prior to sealing and pressurizing the tube blank.
 7. Theapparatus for bending a tube blank of claim 1 further including tubeblank preforming means, a portion of which revolves proportionally withsaid shoe around said axis, for preforming a desired profile in a thirdportion of the blank outwardly from the second portion of the blank. 8.The apparatus for bending a tube blank of claim 7 further including abase and wherein said moving means includes a wing mounted to said baseto revolve about said axis, wherein said preforming means includes acontoured outer die mounted for reciprocal sliding movement on aid wingand a cooperating, inner preforming die, said inner preforming die andsaid outer die adapted to close around the third portion of the blank,thereby preforming the third portion, after the blank has been bentaround said outer surface.
 9. The apparatus for bending a tube blank ofclaim 8 wherein said inner bending die and said inner preforming die areintegrally connected.
 10. The apparatus for bending a tube blank ofclaim 9 further including sealing means for sealing the blank and forhydraulically pressurizing the interior of the blank to a desiredpressure while said moving means moves said shoe and while said outerdie and said inner preforming die close around the third portion of theblank.
 11. The apparatus for bending a tube blank of claim 10 whereinthe tube blank has first and second opposing ends and wherein saidsealing means includes a pair of tools having bores, said tools beingadapted to telescopically extend over said ends to seal and pressurizethe tube blank.
 12. The apparatus for bending a tube blank of claim 11wherein said sealing means are mounted to said wing to rotate therewitharound said axis.
 13. The apparatus for bending a tube blank of claim 10further including filling means for automatically filling the tube blankwith liquid prior to sealing and pressurizing the tube blank.
 14. Theapparatus for bending a tube blank having an outer diametercomprising:an inner bending die having an arcuate outer surface whichhas a first radius from an axis; a wiper shoe having an inner surface,said shoe disposed and adapted to trap a tube blank between said innersurface and said outer surface said inner and outer surfaces each definea mutually cooperating mold cavity sized to completely enclose a portionof the blank; holding means for holding a first portion of the blankagainst said inner die; limiting means for limiting movement of saidshoe to rolling about an arc around said axis, said arc having a secondradius from said axis which is approximately between said first radiusand said first radius plus said diameter, said second radius beingapproximately equal to said first radius, said limiting means includinga stationary pinion coaxial with said axis and a rack rigidly connectedto said shoe and tangentially engaged with said pinion; sealing meansfor sealing the blank and for hydraulically pressurizing the interior ofthe blank to a desired pressure while said moving means moves said shoe,the tube blank has first and second opposing ends and wherein saidsealing means includes a pair of tools having bores, said tools beingadapted to telescopically extend over said ends to seal and pressurizethe tube blank; and filling means for automatically filling the tubeblank with liquid prior to sealing and pressurizing the tube blank.